Wideband Inhomogeneous-Polarizer Loaded Circularly Polarized SIW Horn Antenna for Broadband Millimeter-Wave Applications

An inhomogeneous-polarizer loaded substrate integrated waveguide (SIW) horn antenna is proposed to obtain wideband circularly polarized (CP) radiation. First, by introducing extended substrate and extra dielectric slabs around the horn radiating aperture, broadband impedance matching of the SIW horn can be realized. Then, a pure dielectric near-field CP polarizer is designed and placed in front of the horn to obtain broadband CP radiation. The polarizer is designed to feature inhomogeneous property for different polarization orientation illuminations. With this property, 90 degrees phase difference for a pair of orthogonal linearly polarized waves can be realized. Two methods are utilized to analyze the inhomogeneous property of the polarizer and to provide detailed parameter estimation steps/formulas. The effects of polarizer size and oblique incidence are also studied, and a very wide 3 dB axial-ratio beamwidth of 104 degrees is achieved. Measured results indicate that the proposed CP SIW horn can obtain a matching bandwidth greater than 40% (22-34 GHz) and a CP radiation bandwidth of 30% (22-29.8 GHz). Simple structure and wideband CP performance make it an attractive candidate for broadband millimeter-wave applications.